Amino acid chelates are generally produced by the reaction between α-amino acids and metal ions having a valence of two or more to form a ring structure. In such a reaction, the positive electrical charge of the metal ion can be neutralized by the electrons available through the carboxylate or free amino groups of the α-amino acid.
Traditionally, the term “chelate” has been loosely defined as a combination of a polyvalent metallic ion bonded to one or more ligands to form a heterocyclic ring structure. Under this definition, chelate formation through neutralization of the positive charge(s) of the metal ion may be through the formation of ionic, covalent, or coordinate covalent bonding. An alternative and more modern definition of the term “chelate” requires that the polyvalent metal ion be bonded to the ligand solely by coordinate covalent bonds forming a heterocyclic ring. In either case, both are definitions that describe a metal ion and a ligand forming a heterocyclic ring.
Chelation can be confirmed and differentiated from mixtures of components by infrared spectra through comparison of the stretching of bonds or shifting of absorption caused by bond formation. As applied in the field of mineral nutrition, there are certain “chelated” products that are commercially utilized. One product is referred to as an “amino acid chelate.” When properly formed, an amino acid chelate is a stable product having one or more five-membered rings formed by a reaction between the amino acid and the metal. The American Association of Feed Control Officials (AAFCO) has also issued a definition for amino acid chelates. It is officially defined as the product resulting from the reaction of a metal ion from a soluble metal salt with amino acids having a mole ratio of one mole of metal to one to three (preferably two) moles of amino acids to form coordinate covalent bonds. The products are identified by the specific metal forming the chelate, e.g., iron amino acid chelate, copper amino acid chelate, etc.
In further detail with respect to amino acid chelates, the carboxyloxygen and the α-amino group of the amino acid each bond with the metal ion. Such a five-membered ring is defined by the metal atom, the carboxyloxygen, the carbonyl carbon, the α-carbon, and the α-amino nitrogen. The actual structure will depend upon the ligand to metal mole ratio and whether the carboxyloxygen forms a coordinate covalent bond or a more ionic bond with the metal ion. Generally, the amino acid to metal molar ratio is at least 1:1 and is preferably 2:1 or 3:1. However, in certain instances, the ratio can be 4:1. Most typically, an amino acid chelate with a divalent metal can be represented at a ligand to metal molar ratio of 2:1 according to Formula 1 as follows:
In the above formula, the dashed lines represent coordinate covalent bonds, covalent bonds, or ionic bonds. Further, when R is H, the amino acid is glycine, which is the simplest of the α-amino acids. However, R could be representative of any other side chain that, when taken in combination with the rest of the amino acid structure(s), results in any of the other twenty or so naturally occurring amino acids that are typically derived from proteins. All of the amino acids have the same configuration for the positioning of the carboxyloxygen and the α-amino nitrogen with respect to the metal ion. In other words, the chelate ring is defined by the same atoms in each instance, even though the R side chain group may vary.
The reason a metal atom can accept bonds over and above the oxidation state of the metal is due to the nature of chelation. For example, at the α-amino group of an amino acid, the nitrogen contributes to both of the electrons used in the bonding. These electrons fill available spaces in the d-orbitals forming a coordinate covalent bond. Thus, a metal ion with a normal valency of +2 can be bonded by four bonds when fully chelated. In this state, the chelate is completely satisfied by the bonding electrons and the charge on the metal atom (as well as on the overall molecule) can be zero. As stated previously, it is possible that the metal ion can be bonded to the carboxyloxygen by either coordinate covalent bonds or more ionic bonds.
The structure, chemistry, bioavailability, and various applications of amino acid chelates are well documented in the literature, e.g. Ashmead et al., Chelated Mineral Nutrition, (1982), Chas. C. Thomas Publishers, Springfield, Ill.; Ashmead et al., Intestinal Absorption of Metal Ions, (1985), Chas. C. Thomas Publishers, Springfield, Ill.; Ashmead et al., Foliar Feeding of Plants with Amino Acid Chelates, (1986), Noyes Publications, Park Ridge, N.J.; U.S. Pat. Nos. 4,020,158; 4,167,564; 4,216,143; 4,216,144; 4,599,152; 4,725,427; 4,774,089; 4,830,716; 4,863,898; 5,292,538; 5,292,729; 5,516,925; 5,596,016; 5,882,685; 6,159,530; 6,166,071; 6,207,204; 6,294,207; 6,458,981, 6,518,240, 6,614,553; each of which is incorporated herein by reference.
One advantage of amino acid chelates in the field of mineral nutrition is attributed to the fact that these chelates are readily absorbed from the gut and into mucosal cells by means of active transport. In other words, the minerals can be absorbed along with the amino acids as a single unit utilizing the amino acids as carrier molecules. Therefore, the problems associated with the competition of ions for intestinal absorption sites and the suppression of specific nutritive mineral elements by others can be avoided.
Many persons suffer from various allergies, which can be caused by ingesting food, liquids, or supplements containing allergens. Although the biochemistry of allergic reactions is not precisely understood, it is believed that the allergens cause, upon ingestion or other contact with the body, a specific reagin to be formed in the bloodstream. A response to an allergen by some is thought to be an inherited characteristic. In a person that is allergic to a specific allergen, the allergen, which is often a protein, can be regarded as a key which fits the corresponding structural shape of the reagin molecule.
Allergic reactions can result in symptoms ranging from very mild to very severe, some of which can cause death. For example, symptoms, both mild and severe, include skin rashes (allergic eczema and urticaria), dermal symptoms, respiratory symptoms (including allergic rhinitis and bronchial asthma), gastrointestinal symptoms, and migraine headaches. Violent illnesses have been known to include shock-like reactions, vascular collapse, and allergic anaphylaxis.
As amino acids used to prepare amino acid chelates are typically derived from protein hydrolysis, such amino acids can cause allergic reactions in a small percentage of the population. As a result, it would be an advancement in the art to provide hypoallergenic amino acid chelates and hypoallergenic formulations that contain amino acid chelates in order to avoid undesired allergic reactions.